1. Field of the Invention
A method a process involving the application of a labile organic substrate, and optionally sulfate, to a soil and ground water supply for the express purpose of stimulating reactive sulfate reduction to facilitate the formation of mineral iron sulfides that abiotically treats soil contaminants, including chlorinated compounds, and hexavalent chromium or other oxidized or partially oxidized organic and inorganic contaminants, with an iron sulfide microbial geochemical treatment zone. Other iron sulfide compounds, or generally FexSy, may also comprise the treatment zone in addition to iron monosulfide including activated iron or other metals which may be formed by microbial geochemical processes. The process also includes, in some cases, the supplementation of reactive sulfate to ground water where insufficient natural supply exists, wherein a solution of organic and dissolved reactive sulfate introduced to the soil and ground water, the introduction of reactive sulfate tailored to the individual site conditions to meet contaminant mass constraints.
2. Description of Prior Art
The following United States patents are identified and disclosed herein. Several devices are disclosed relating to the chemical treatment of ground and water contaminants, but none of them are or may be adapted to define the stated method or process of the current invention, nor do they utilize the same chemicals, reactions and process a does the current invention.
In U.S. Pat. No. 5,362,402 to Haitko, a method for the dehalogenation of halongenated hydrocarbons using metallic iron in the presence of citric acid, primarily in aqueous solutions. Addition of agitated iron particles in an aqueous solution containing hexavalent and trivalent chromium forming an insoluble precipitate is the objective of the disclosed method of U.S. Pat. No. 5,380,441 to Thornton, and also the relative subject matter of U.S. Pat. No. 5,427,692 to Thornton, but including the use of barium nitrate.
Use of iron powder and a water soluble weak acid inorganic compound which does not contain nitrogen or phosphorus to decontaminate soil infused with a halogenated organic compound is disclosed in U.S. Pat. No. 6,068,777 to Kimura, which is adapted primarily for the treatment of groundwater. Hexavalent chromium is the target contaminant in the method and process in U.S. Pat. No. RE 36,915 to Suciu, which uses the addition of a ferrous ion and a sulfide ion to a stream of waste water prior to disposal reducing the hexavalent chromium to trivalent chromium, which forms a precipitate in the waste water creating a sludge, the process also including the addition of a flocculating polymer to induce the formation of the precipitant.
Also disclosed are three articles, the first co-authored by the inventor, indicated as follows. In a first article, (Kennedy, L. G. and Everett, J. W., 2001. Microbial degradation of simulated landfill leachate: Solid iron/sulfur interactions; Applied Environmental Research, Vol. 5, No. 2, pgs. 103-116.) the focus of the article dealt primarily with the formation of reduced iron and sulphur minerals to assess organic contaminant degradation due to Fe+3 and SO42− microbial reduction process, but did not disclose any resultant method or process dealing with chlorinated solvent reduction in the soil or groundwater.
In the article by Butler, E. C. and Hayes, K. F., 1999. Kinetics of the transformation of trichloroethylene and tetrachloroethylene by iron sulfide; Environmental Science Technology, Vol. 33, No. 12, pgs. 2021-2027, laboratory process for the degradation of PCE an TCE are discussed, but without disclosure of a method or process for naturally forming the iron sulfide using the disclosed process creating the iron sulfide barrier as a microbial geochemical treatment zone. Another collaterally related scholarly article is found in the article, Parker, T. and Mohr, T., Symposium on natural attenuation of chlorinated solvents in groundwater—a summary; Hydro Vision Online Newsletter, Volume 5, No. 4, Winter 1996; www.grac.org/winter96/rnapaper.htm, dealing with chlorinated solvent plume movement, migration and activity.
In Applicant's article, See Kennedy, supra., preliminary research and testing is documented dealing with the use of solid electron acceptors, including CaSO42− and Fe(OH)3, to promote carbonate and sulfide mineral formation to control greenhouse gas production, including carbon dioxide and methane, with the suggestion that the Fe and S mineral could also be used to assess organic contaminant degradation occurring due to Fe3+ and SO42− microbial reduction processes for natural attenuation studies. The current invention is a result of such studies, and is the method for creating an iron monosulfide (FeS) microbial geochemical treatment zone for areas having previously experienced soil and ground contamination with toxic chemical solvents and by-products.